Cholinesterases of marine teleost fish: enzymological characterization and potential use in the monitoring of neurotoxic contamination

Acetylcholinesterase (AChE) is well established as a biomarker of exposure to organophosphate compounds in freshwater fish. By constrast, only a few studies on the enzymology and responsiveness of AChE are available for marine species. In this study, we report characteristics of cholinesterases from brain and muscle tissue of three marine teleosts, Limanda limanda, Platichthys flesus and Serranus cabrilla, to provide basal information for environmental monitoring in coastal and marine areas. In brain, cholinesterase activity was exclusively comprised of AChE. In contrast, both butyrylcholinesterase (BChE) and AChE were present in axial muscle. The fish BChEs displayed atypical substrate and inhibitor specificities in that they cleaved acetyl-beta-(methyl)thiocholine and were sensitive to BW284C51. Bimolecular inhibition constants, K-i, of BChE for the organophosphates paraoxon and dichlorvos were more than three orders of magnitude greater than the respective K-i values of AChEs. This reflects a much higher sensitivity of BChE to the organophosphates than AChE. Neither AChE from muscle and brain within one species, respectively, nor corresponding cholinesterases from different species differed significantly in their K-i values. The presence of two cholinesterases of differential sensitivity in the same tissue is potentially useful in monitoring. (C) 1999 Elsevier Science Ltd. All rights reserved.